Correct Answer - Option 1 : 768
Given:
The average salary of all staff is 8000
The average salary of 12 technical staff is 72000
The average salary of non-technical staff is 7000
Formula used:
Average = (Sum of all observations)/(Total number of observations)
Calculation:
Let the number of non-technical staff be x
⇒ Total staff = (12 + x)
The total salary of staff = The average salary of total staff × Total number of staff
The average salary of all staff is 8000
⇒ The total salary of staff = 8000 × (12 + x)
The average salary of 12 technical staff is 72000
⇒ The total salary of technical staff = 72000 × 12
The average salary of x non-technical staff is 7000
⇒ The total salary of non-technical staff = 7000x
The total salary of all staff = Total salary of technical staff + Total salary of non-technical staff
⇒ 8000 × (12 + x) = 72000 × 12 + 7000x
⇒ 8(12 + x) = 72 × 12 + 7x
⇒ 96 + 8x = 864 + 7x
⇒ x = 864 - 96
⇒ 768
∴ The number of non-teachnical staff is 768